GLOSSARY

The terms in this glossary were compiled from numerous sources. Some definitions have been modified and may not be the only valid ones for these terms.

Algae—Chlorophyll-bearing nonvascular, primarily aquatic species that have no true roots, stems, or leaves; most algae are microscopic.

Aquatic-life criteria—Water-quality guidelines for protection of aquatic life. Often refers to U.S. Environmental Protection Agency water-quality criteria for protection of aquatic organisms. See also Water-quality standards.

Aquatic invertebrates—Insects, worms, crayfish, snails, clams, and other organisms without a backbone that live in, on, or near lakes, streams, rivers, or oceans.

Aquifer—A water-bearing layer of soil, sand, gravel, or rock that will yield usable quantities of water to a well.

Base flow—Sustained, low flow in a stream; ground-water discharge is the source of base flow in most streams.

Basic-fixed site—A site on a stream where streamflow and water-quality data are collected to measure how often and how much of a constituent is found, over time, due to different seasonal, hydrologic, or land-use patterns.

Basin—See Drainage basin.

Bed sediment—The material that temporarily is stationary in the bottom of a stream or other watercourse.

Benchmark site—See reference site.

Best management practices (BMPs)—Land-use practices that are effective and practical ways of preventing or reducing nonpoint-source pollution.

Blue-baby syndrome—A condition that can be caused by ingestion of high amounts of nitrate, resulting in the blood losing its ability to effectively carry oxygen. Most common in young infants and elderly people.

Confined aquifer—An aquifer that is completely filled with water under pressure and that is overlain by material that restricts the upward movement of water.

Contamination—Degradation of water quality compared to original or natural conditions due to human activity.

Contributing area—The area in a drainage basin that contributes water to streamflow or recharge to an aquifer.

Denitrification—A process by which oxidized forms of nitrogen such as nitrate (NO₃) are reduced to form nitrites, nitrogen oxides, ammonia, or free nitrogen, commonly brought about by the action of bacteria and usually resulting in the los of nitrogen to the air.

Drainage basin—The portion of the surface of the Earth that contributes water to a stream through overland runoff, including tributaries and impoundments.

Drinking-water standard or guideline—A threshold concentration of a chemical constituent or compound in a public drinking-water supply, designed to protect human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contamination levels for public water systems required to protect the public welfare; guidelines have no regulatory status and are issued in an advisory capacity.

Ecological synoptic study—A short-term investigation to measure the differences in biologic communities, within all or part of a study area, due to different factors, such as land uses or contaminant sources.

Flow path—An underground route for ground-water movement, extending from a recharge area to a discharge area or point such as a shallow stream or pumping well.

Flowpath survey—Collection of data from a network of wells in an area to study the relations among land-use practices, ground-water flow, and contaminant occurrence and transport. These surveys are conducted in the area of one of the land-use surveys.

Human health advisory—Guidance provided by U.S. Environmental Protection Agency, State agencies or scientific organizations, in the absence of regulatory limits, to describe acceptable contaminant levels in drinking water or edible fish.

Index of Biotic Integrity (IBI)—An aggregated number, or index, based on several measures of a fish community that provides an assessment of biological conditions.

Indicator site—Stream sampling site located at an outlet of a drainage basin with relatively homogeneous land use and physiographic conditions; drainage areas range from 20 to 200 square miles.

Integrator or mixed-use site—Stream sampling site located at an outlet of a drainage basin that contains multiple environmental settings. Most integrator sites are on major streams with relatively large drainage areas.

Intensive-fixed site—A basic-fixed site at which sampling frequency is increased during selected seasonal periods.

Intolerant species—Species that are not adaptable to human alterations to the environment and thus decline in numbers where human alterations occur.

Land-use survey—Collection of data from a network of shallow wells in an area having a relatively uniform land use. These studies have the goal of relating the quality of shallow ground water to land use.

Leaching—The removal of materials in solution from soil or rock to ground water; refers to movement of pesticides or nutrients from land surface to ground water.

Major ions—Constituents commonly present in water at concentrations exceeding 1.0 milligram per liter. Generally includes the cations calcium, magnesium, sodium, and potassium; the anions, sulfate, chloride, fluoride, and nitrate; and those constituents contributing to alkalinity, most generally bicarbonate and carbonate.

Maximum contaminant level (MCL)—Maximum permissible level of a contaminant in water that is delivered to any user of a public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency.

Metabolite—A substance produced as the result of the degradation of another compound.

Milligrams per liter (mg/L)—A unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water; equivalent to one part per million. One thousand micrograms per liter equals 1 mg/L.

Minimum reporting level (MRL)—The smallest measured concentration of a constituent that may be reliably reported as a result of use of a given analytical method.

Nonpoint source—A source that cannot be defined as originating from discrete points such as pipe discharge. Areas of fertilizer and pesticide applications, atmospheric deposition, manure, and natural inputs from runoff are types of nonpoint sources.

Nutrient—Element or compound essential for animal and plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

Organochlorine compound—Synthetic organic compounds containing chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine.

Organochlorine insecticide—Organic insecticides containing a high percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as chlordane), and chlorinated benzenes (such as lindane). Use of most organochlorine insecticides was banned because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.

Physiography—A description of the surface features of the Earth, with an emphasis on the origin of landforms.

Point source—A source that originates from a discrete location such as discharge pipe or ditch, well, concentrated livestock operation, leaky tank, or floating craft.

Polychlorinated biphenyls (PCBs)—A mixture of chlorinated derivatives of biphenyl, marketed under the trade name Aroclor. PCBs were used in transformers and capacitors for insulating purposes and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979.

Polycyclic aromatic hydrocarbon (PAH)—Organic compounds with a fused-ring aromatic structure. PAHs result from incomplete combustion of organic carbon, municipal solid waste, and fossil fuels, as well as from uncombusted coal and oil products.

Probable effect level (PEL)—Concentration of a contaminant above which adverse biological effects are expected to occur frequently.

Recharge—Water that infiltrates the ground and reaches the saturated zone or aquifer.

Reference site—A site whose contributing area is minimally disturbed, such as forest and other natural areas.

Riparian—Areas adjacent to rivers and streams with a high density, diversity, and productivity of plant and animal species relative to nearby uplands.

Runoff—Excess rainwater or snowmelt that is transported to streams by overland flow, tile drains, or ground water.

Sorption—General term for the interaction (binding or association) of a solute ion or molecule with a solid.

Species diversity—An ecological concept that incorporates both the number of species in a particular sampling area and the evenness with which individuals are distributed among the various species.

Species (taxa) richness—The number of species (taxa) present in a defined area or sampling unit.

Subunit survey—Collection of data from a network of wells in a major aquifer system, based primarily existing wells and on data collected in other programs.

Synoptic site—A site sampled during a short-term investigation to measure differences in water quality, within all or part of a study area, due to different factors, such as land uses or contaminant sources.

Threshold effect level (TEL)—Concentration of a contaminant above which adverse biological effects are expected to occur rarely.

Tolerant species—Those species that are adaptable to (tolerant of) human alterations to the environment and often increase in number when human alterations occur.

Trace element—An element found in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment; examples include arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.

Unconfined aquifer—An aquifer whose upper surface is a water table. See confined aquifer.

Unconsolidated deposit—Deposit of loosely bound sediment that typically fills topographically low areas.

Urban gradient study—A study designed to measure physical, chemical, and biological responses along gradients of urban land-use intensity and identify the factors most responsible for controlling water-quality conditions.

Volatile organic compounds (VOCs)—Organic chemicals that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, and some by-products of chlorine disinfection.

Water-quality standards—State-adopted and U.S. Environmental Protection Agency-approved ambient standards for water bodies. Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.

Watershed—See Drainage basin.

Water table—The point below land surface where ground water is first encountered and below which the earth is saturated. Depth to a water table varies widely.

Water year—The continuous 12-month period, October 1 through September 30, designated by the year in which it ends. September 30, 1980 is the "1980" water year.